C4 core questions
Unit 4 – Chemical Changes – core questions
Question
Answer
What is the reactivity series?
A list of metals ordered by their reactivity
How can the order of reactivity for specific metals be found?
Add the metals to water or acid and see which ones react the most (by how much fizzing there is)
What is the name for a reaction where oxygen is added to form a compound?
Oxidation
What is the name for a reaction where oxygen is removed from a compound?
Reduction
Which metals do not react with acids?
Copper, silver, gold as they are less reactive than hydrogen
Explain why zinc can be extracted from zinc oxide with carbon but magnesium cannot be extracted from magnesium oxide with carbon
Magnesium is more reactive than carbon, Zinc is less reactive than carbon, Carbon can therefore remove oxygen from zinc oxide but not magnesium oxide
Explain why silver can be found pure in the Earth's crust
It is very unreactive
What process is used to extract metals less reactive than carbon?
Reduction with carbon
Which metals are extracted by reduction with carbon?
Iron, Zinc and Copper
What process is used to extract metals more reactive than carbon?
Electrolysis
Define an ore
A rock containing enough metal in it for it to be economically worthwhile to extract the metal.
Define a displacement reaction
A reaction in which a more reactive element takes the place of a less reactive element
Define oxidation in terms of electrons
Oxidation is the loss of electrons
Define reduction in terms of electrons
Reduction is the gain of electrons
Which of the substances below has been oxidized and which has been reduced? Al³⁺ + Fe → Fe³⁺ + Al
Aluminium has been reduced and iron has been oxidised
Show two half equations for the reaction below: Al³⁺ + Fe → Fe³⁺ + Al
Al³⁺ + 3e⁻ → Al, Fe → Fe³⁺ + 3e-
Define acid in terms of pH
A substance with a pH of less than 7
Define acids in terms of ions
A substance which releases H⁺ ions in solution
What does (aq) stand for?
Aqueous: when something is dissolved in water
State the three common acids and give their formulae
Hydrochloric acid,HCl, Sulphuric acid,H₂SO₄, Nitric acid,HNO₃
What is the formula of the carbonate ion?
CO32-
What is the formula of the sulphate ion?
SO42-
What is the formula of the nitrate ion?
NO3-
What is the formula of the hydroxide ion?
OH-
What is a neutral solution?
A solution with a pH of 7. Water is an example.
How do you measure pH?
With an indicator or pH probe.
What is a base?
A metal oxide, hydroxide or carbonate, they react with acids.
What is an alkali?
A soluble base. E.g. sodium hydroxide
Which ions are always present in a solution of an alkali?
OH⁻
What is a salt?
An ionic compound formed during neutralisation
What type of salts are formed by the three main acids?
Hydrochloric acid produces chlorides, sulphuric acid = sulphates, nitric acid = nitrates
What is a neutralisation reaction?
A reaction involving an acid that results in a neutral solution
Which ions react together in a neutralization reaction?
H⁺ and OH⁻
Write the equation showing the reaction between H⁺ and OH⁻ ions
H⁺ + OH⁻ → H2O
metal + acid →
→ salt + hydrogen gas
metal hydroxide + acid →
→ salt + water
metal oxide + acid →
→ salt + water
metal carbonate + acid →
→ salt + water + carbon dioxide
How do you make a pure salt from an acid?
React the acid with a excess base then filter off the excess base. E.g. to make copper sulphate react copper oxide with sulphuric acid
If a salt is in solution, how do you extract it as a solid?
Allow the water to evaporate off and it will leave the salt behind as a solid.
What is a strong acid?
An acid which completely ionises in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻
What is a weak acid?
An acid which only partially ionises in water. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H⁺ ions.
What is the link between the strength of an acid and its pH?
As an acid increases in strength the pH decreases.
What is a concentrated acid?
An acid where there are lots of acid particles in the water.
What is a dilute acid?
An acid where there are fewer acid particles in the water.
What is pH a measure of?
pH is measure of concentration of H⁺ in a solution.
If the pH increases by 1 what does this mean has happened to the H+ ion concentration?
It has decreased by a factor of 10
Is this process oxidation or reduction? Al → Al³⁺ + 3e⁻
Oxidation
Is this process oxidation or reduction? Na⁺ + e⁻ → Na
Reduction
What is electrolysis?
Using electricity to break down a substance
What happens to an ionic substance when it is melted or dissolved in water?
The ions become free to move around
What is an electrolyte?
A solution or liquid containing ions
Which electrode do negative ions move to?
Cathode (positive electrode)
Which electrode do positive ions move to?
Anode (negative electrode)
Balance the equation: Al3+ + e⁻ → Al
Al3+ + 3e⁻ → Al
Balance the equation: Cl⁻ → Cl2+ e⁻
2Cl⁻ → Cl2 + 2e⁻
Balance the equation: O2- → O2 + e⁻
2O2- → O2 + 4e⁻
What will be the products for the electrolysis of molten iron bromide?
Iron and bromine
What will be the products of electrolysis of molten zinc oxide?
Zinc and oxygen
If electrolysis of a solution containing a metal more reactive than hydrogen is carried out what forms at the cathode?
Hydrogen
If electrolysis of a solution containing sulphate, carbonate or nitrate ions what is produced at the anode?
Oxygen
What is the main disadvantage of using electrolysis to extract metals?
Requires a large amount of energy to melt the compounds and to produce the necessary electricity
Why is aluminium oxide mixed with cryolite when extracting aluminium?
To lower the melting point
What is produced at the anode and cathode in the electrolysis of aluminium oxide?
Aluminium at the cathode and oxygen at the anode
Why does the anode need to be replaced in the electrolysis of aluminium oxide?
The oxygen reacts with the carbon electrode to produce carbon dioxide.
In the electrolysis of sodium chloride solution, what are the products?
Chlorine gas and hydrogen gas
Why is sodium not produced in the electrolysis of sodium chloride solution?
It is more reactive than hydrogen so hydrogen is produced instead.
In the electrolysis of lithium sulphate solution, what are the products?
Chlorine gas and oxygen gas